Thixotropic Behaviour of a Cu – Eutectic Sn-Pb Slurry

Semi-solid materials (SSM) in the thixotropic state behave like liquids, i.e they show low or null shear resistance and, at the same time, they behave like solids as do not fall to pieces under applied forces. At present, the potential advantages and industrial applications of these materials are well recognized, in particular for the production of Al-alloy components for the aerospace and automotive sectors. This work is focused on the evaluation and characterization of the thixotropic behaviour of a metal mixture in the semi-solid state obtained by “Compocasting”. The mixture is obtained by mixing spherical solid Cu particles with a liquid eutectic tin-lead alloy. Measurements of the time-dependence of the viscosity of the mixture using an instrumented rheometer showed that, after mechanical stirring, the slurry acquires thixotropic properties. The best conditions to obtain such mixture are presented. Additionally, once the mixture is cooled down, the material is reheated and then tested in a laboratory backward extrusion process. The behaviour of the material is analysed on the basis of the microstructure obtained, and the process parameters considered.